Processes for recovering cesium from cesium-containing materials such as pollucite and other cesium-containing minerals have been reported in the technical literature.
One process which is reported involves leaching ground pollucite ore with strong sulfuric acid to obtain an extract containing cesium alum, which is recovered by crystallization.
Cesium alum is cesium aluminum sulfate hydrate. Its formula can be empirically expressed as CsAl(SO.sub.4).sub.2 .cndot.12H.sub.2 O, or Cs.sub.2 SO.sub.4 .cndot.Al.sub.2 (SO.sub.4).sub.3 .cndot.24H.sub.2 O. The cesium alum contained in or crystallized from the sulfuric acid extracts of pollucite is typically contaminated with other metal ions such as rubidium, sodium, potassium, magnesium, and iron.
The cesium alum is then redissolved in water at an elevated temperature and reacted with an alkaline earth metal hydroxide, such as barium hydroxide or calcium hydroxide, to form an aluminum hydroxide precipitate together with precipitated barium sulfate or calcium sulfate. The cesium alum may alternatively be reacted with ammonia to precipitate the aluminum as aluminum hydroxide. The cesium sulfate remains in the supernatant solution. The cesium can be recovered from the supernatant solution and converted into other cesium compounds.
U.S. Pat. No. 3,207,571 to Berthold discloses an improved process for producing cesium compounds from cesium aluminosilicate ore. In the process disclosed by Berthold, finely ground pollucite ore and the stoichiometric quantity of sulfuric acid required for reaction with the alkali metals and aluminum present in the ore are heated to a temperature of about 150.degree. Celsius for a period of about four hours, and a weight of water equal to one-fourth the weight of the pollucite ore used is added to the ore-acid mixture during the heating period to substantially completely extract the cesium from the ore as cesium alum. The mixture is filtered and the filtered cesium alum is then crystallized a number of times. The crystallized cesium alum is then added to a hot slurry of calcium hydroxide in distilled or demineralized water to yield a solution of cesium sulfate and a solid residue of calcium sulfate hydrate and aluminum hydroxide. The calcium hydroxide is added to the cesium alum in a quantity stoichiometrically sufficient to convert all of the cesium alum to cesium sulfate and aluminum hydroxide. The insoluble substances are separated from the cesium sulfate solution.
Berthold discloses that cesium sulfate can be recovered by evaporating the solution to dryness and calcining the salt so obtained at about 300.degree. Celsius to remove the last traces of water. Conversion of cesium sulfate to other cesium salts can be accomplished by adding an aqueous barium hydroxide mixture to the cesium sulfate liquor. The resulting mixture is then separated to yield a solution of cesium hydroxide. Berthold provides that the cesium hydroxide can be converted to a desired cesium salt by acidification with the desired acid. To obtain a salt other than the sulfate or hydroxide, Berthold alternatively mentions treating the cesium sulfate solution with the barium salt of the desired acid.
German Patent DE 43 13 480 of Hoffmann et al. discloses a process which avoids the use of barium compounds in the production of cesium salts from cesium alum. Cesium alum is reacted with calcium hydroxide, in an amount which is equimolar to the aluminum, and with a highly water soluble calcium salt, in an amount which is equimolar to the cesium. This process results in a product containing soluble calcium sulfate and magnesium.
One known use for cesium compounds is in high specific gravity drilling fluids for oil and gas wells. Bore hole turnings are known to slow or stop the drilling process, and in some cases, plug the porous strata of the bore hole. Feedback data on the bore hole condition is limited in the regions of plugged strata thereby reducing the effectiveness of the drilling operation. Another problem which may occur is the incompatibility of impurities found in cesium compounds with the various solutions, viscosifiers, and additives used in drilling fluids. For example, the presence of divalent impurities like calcium in cesium compounds may degrade the polymers present in the viscosifiers. The presence of divalent impurities is particularly harmful in high temperature and high pressure applications commonly found in deep well drilling where the viscosifier functions to suspend the bore hole turnings and act as a drilling lubricant. High density fluids having a specific gravity of about 1.8 and above have been used to convey the turnings to the surface. For wells having a depth greater than one mile, zinc bromide and mixtures with other salts have been utilized to improve the performance of the fluids. However, the nature of these materials renders them somewhat undesirable. One material which has been defined as a replacement for zinc bromide is cesium formate. Blends of cesium formate with other alkali metal formates are also known. See European Patent No. 572 113.
Cesium salts produced by the above described processes, however, do not avoid the problem of side reaction precipitates formed between divalent and multivalent cationic impurities and the carbonates present in the drilling environment or the corrosion effect of drilling equipment materials caused by sulfate and chloride ion impurities. In addition, the processes described above are relatively difficult and expensive for commercial application.
Therefore, there has been a recognized need for a cesium compound having a substantially reduced level of divalent and multivalent cation impurities and sulfate and chloride ions and an improved process for its preparation.